1. Field of the Invention
This invention pertains to a process for manufacturing minute capsules, en masse, in a liquid manufacturing vehicle. The process involves liquid-liquid phase separation of a relatively concentrated solution of polymeric material to be used in the formation of walls for the minute capsules.
En masse processes for the manufacture of microcapsules have generally required large amounts of liquid manufacturing vehicle and have generally resulted in low yields of capsules. An encapsulating system and process which utilizes relatively small amounts of manufacturing vehicle to generate relatively large amounts of microcapsules would be valuable from several viewpoints. For example, costs of transporting the capsule product, as manufactured, would be reduced because the product contains less vehicle. As another example, in the case where the capsule product is to be coated to a dried film on a sheet substrate coating costs are reduced because there is less liquid vehicle to be removed from the substrate.
Many combinations of materials have been used in the past in search of compositions which yield certain physical characteristics in capsule walls or which permit performing the encapsulating process under certain desired or required conditions. As examples of desirable capsule characteristics, small size, impermeability of capsule walls to diffusion and strength of capsule walls to withstand normal handling forces can be mentioned. As examples of desirable process conditions, relatively high pH, relatively short times, and relatively high yield and concentration are important.
It is, therefore, an object of the present invention to provide a capsule manufacturing process wherein capsules are produced in high yield and in increased concentration. It is, additionally, an object of the invention to provide a process which requires a relatively short time for completion and which utilizes process conditions of increased convenience.
It is, further, an object of the present invention to provide a process for manufacturing microcapsules, which microcapsules have capsule walls of increased impermeability. Additionally, it is an object of this invention to provide a process for manufacturing very small capsules having predominantly single-particle capsule core entities.
Specifically, it is an object of this invention to provide an encapsulating process wherein the capsule wall material comprises a polymer formed from a urea-formaldehyde, dimethylol urea or methylated dimethylol urea starting material wherein said wall material is generated by an in situ condensation reaction. It is, further, an object of this invention to provide such capsule wall material by an improved condensation reaction conducted in the presence of a negatively-charged, carboxyl-substituted, linear aliphatic hydrocarbon polyelectrolyte material dissolved in the capsule manufacturing vehicle.
2. Description of the Prior Art
South African Pat. No. 62/939 issued Mar. 6, 1972 and corresponding in most respects to U.S. Pat. No. 3,516,941, discloses a preparation of microcapsules by in situ polymerization of amides or amines and aldehydes. There is no disclosure of the use of a negatively-charged polyelectrolyte material to modify or otherwise affect the polymerization reaction or product. U.S. Pat. No. 3,516,941 contains disclosure of detrimental effects found in such encapsulating processes when certain wetting agents are used.
U.S. Pat. No. 3,755,190 issued Aug. 28, 1973 discloses a microencapsulating process wherein the capsule wall material is polyhydroxy phenolic/aldehyde polymeric material generated in the presence of poly(vinyl alcohol).
U.S. Pat. No. 3,726,803 issued Apr. 10, 1973 discloses microcapsules having a composite capsule wall structure of hydrophilic polymeric material interspersed by a hydrophobic polymeric material. The hydrophobic polymeric material is disclosed to be an in situ-generated condensate of a polyhydroxy phenolic material and an aldehyde.
U.S. Pat. No. 3,016,308 issued Jan. 9, 1962 discloses encapsulation by continued polymerization of urea/formaldehyde resin dissolved in an aqueous manufacturing vehicle with a polymeric wetting agent. The process utilizes urea/formaldehyde resin as starting material and a slight amount of wetting agent to maintain an emulsion during the continued polymerization.